Ignition devices, in other words, ignition coils, are used for internal combustion engines for ignition of their fuel. An example of specific structures of such an ignition device is disclosed in Japanese Patent Application Publication No. 2009-299614. The ignition device disclosed in the Patent Application Publication includes an insulating-resin case having an inner chamber, connectors, and a high-pressure tower. The ignition device also includes a transformer and a switching module installed in the inner chamber of the case.
The transformer is comprised of: a looped iron-core module having a longitudinal center core; a primary winding, i.e. a primary coil, wound around the center core; and a secondary winding, i.e. a secondary coil, wound around the primary winding. The iron-core module also has an arched side core magnetically coupled to both ends of the center core; the arched side core is located outside a circumferential part of each of the primary and secondary coils. This forms a closed magnetic path. The switching module is connected between the connectors and the primary winding, and operative to open or close electrical connection between the connectors and the primary winding. The ignition device includes a resin filler filled in the inner chamber of the case. The transformer and the switching module are entirely embedded in the resin filler so as to be hermetically sealed in the resin filler.
The structure of the ignition device disclosed in the Patent Application Publication may make it difficult to exhaust heat generated from the transformer and/or the switching module, resulting in an increase of thermal stress in the resin filler and/or the case against cold stress. This may cause cracks in the resin filler and/or the case.
To address such a problem, an exposure of a part of the arched side core from the case will improve heat dissipation of the ignition device to suppress an increase of thermal stress in the resin filler and/or the case, thus preventing the occurrence of cracks in the resin filler and/or the case (see Japanese Patent Application Publication No. 2012-146896).